The present invention relates to integrated circuit structures and fabrication methods, and is more particularly applicable to formation of a buried oxide layer for silicon-on-insulator technologies.
Silicon on insulator (SOI) plays an important role in IC technology. SOI is used for low power, low voltage IC technology, and can be fabricated in a number of ways.
SIMOX is based on established ion implant technology. A silicon dioxide layer is formed by implanting oxygen through the top surface of a standard bulk wafer. Higher doses produce thicker layers as well as greater crystalline damage to the implanted surface. Because oxygen beam implantation typically is of much higher doses, long implant times are used. However, this decreases throughput, which forces device fabs to use higher beam currents which introduce contamination problems.
An alternative implantation method to manufacture SIMOX-like wafers uses Plasma Immersion Ion Implantation technology to implant oxygen. This process is called Separation by Plasma Implantation of Oxygen, and uses plasmas rather than ion beams to introduce ions in a material and form a buried oxide layer (BOX). This method has generally higher throughput since the entire wafer is implanted at once. However, this method generally introduces more than one species into the material, causing bimodal distributions and non-uniform BOX layers.
The present application discloses, as the preferred embodiment, an innovative method of forming a buried oxide layer (BOX) in a semiconductor material. The preferred embodiment uses a low dose oxygen implant using an ion beam, followed by an oxygen implant using a plasma implanting method. This combination can of course be supplemented with other process steps, such as an anneal between the two implants or after them.
The BOX layer created by the low dose beam implant is made of higher quality because the plasma implant adds oxygen ions, atoms, and molecules at a depth that allows any unoxidized silicon that remain in the BOX region after the beam implant to be oxidized. That is, the extra available oxygen will migrate to form a more uniform layer of stoichiometric SiO2 in the BOX region.
The innovative process can also include internal thermal oxidation with the beam implantation and/or the plasma implantation.
The innovations of the present application can be practiced in several process contexts, such as using anneals, rearranging the order of the beam and plasma implants, and adding any other necessary process steps.
Advantages of the disclosed methods and structures, in various embodiments, can include one or more of the following:
plasma implant is inexpensive supplement to low dose SIMOX for forming high quality BOX;
plasma implant adds oxygen to superficial silicon to prevent depletion of oxygen during BOX formation.